Metformin in overweight adolescents with type 1 diabetes does not improve blood glucose control

US-based research does not support use of metformin for overweight young people with type 1 diabetes.

Giving metformin in addition to insulin does not improve glycaemic control in overweight or obese young people with type 1 diabetes, according to research. In the image, the back of a young obese boy

Giving metformin in addition to insulin does not improve glycaemic control in overweight or obese young people with type 1 diabetes, according to research published in JAMA
on 1 December 2015. 

Researchers found that giving the oral glucose-lowering agent, which is typically used in treating type 2 diabetes as a combination therapy, did not significantly improve glycated haemoglobin (HbA1c) levels after 26 weeks although there was a small improvement at 13 weeks. HbA1c gives clinicians a picture of a patient’s average blood sugar levels over months. 

Some 140 patients aged 12–19 years were involved in the study. All of them had type 1 diabetes for an average of seven years and all were overweight or obese with a body mass index (BMI) within the 94th percentile. Their average daily insulin intake was 1.1U/kg and their mean HbA1C level was 8.8%. Metformin was given to 71 of the patients and 69 received a placebo. 

At 13 weeks, researchers found HbA1c reduction was greater in patients with metformin (-0.2%) than placebo (0.1%; mean difference, -0.3% [95% CI, -0.6% to 0.0%]; P=0.02). But this was not found at 26 weeks when the mean change in HbA1c from baseline was 0.2% in each group (mean difference, 0% [95% CI, -0.3% to 0.3%]; P=0.92). 

At 26 weeks, the total daily insulin per kilogram of body weight was reduced by at least 25% in 23% of metformin patients compared with 1% of patients taking placebo (mean difference, 21% [95% CI, 11% to 32%]; P=0 .003). 

Some 24% of metformin patients and 7% of patients receiving the placebo saw a reduction in their BMI of 10% or more at 26 weeks (mean difference, 17% [95% CI, 5% to 29%]; P=0.01). 

“These results do not support prescribing of metformin to overweight adolescents with type 1 diabetes to improve glycaemic control,” say the researchers, based at the Jaeb Center for Health Research, Tampa, Florida. 

Philip Newland-Jones, a specialist diabetes pharmacist at the University Hospital Southampton NHS Foundation trust, says: “The results that show ‘metformin compared with placebo was associated with reductions in weight gain, body mass index, body fat, and total daily insulin dose’ are in line with the evidence for use in adults.

“A reduction in weight gain and body fat may have much larger implications for individual patients involved in this study and I would suggest there would be limitations to focusing on the specific element of HbA1c without considering the wider holistic benefits to patients involved,” he adds.

Metformin, according to Newland-Jones, is a relatively inexpensive medication and he thinks that only a small improvement in clinical benefit or insulin dose reduction may be needed to achieve cost effectiveness.

“This is a fairly small cohort so it is difficult to draw conclusions but I feel the study has positives to be drawn for this patient group but I would suggest further research and large trials need to be undertaken to understand the potential benefits and negatives of metformin as adjunct therapy in adolescent type 1 diabetes,” he adds. 


[1] Libman IM, Miller KM, DiMeglio LA et al. Effect of metformin added to insulin on glycemic control among overweight/obese adolescents with type 1 diabetes: a randomized clinical trial. JAMA 2015;314(21):2241–2250. doi:10.1001/jama.2015.16174

Last updated
The Pharmaceutical Journal, December 2015;Online:DOI:10.1211/PJ.2015.20200224